Spectroelectrochemistry of Dendrimers: The Radical Cations of Low-Generation PAMAM-Like Dendrimers with a 1,4-Phenylenediamine Core As Studied by Electron Spin Resonance (ESR)/UV鈭扸is NIR Spectroelectr

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• 作者：Michal Zalibera ; Peter Rapta ; Georg Gescheidt ; J酶rn B. Christensen ; Ole Hammerich ; Lothar Dunsch
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：March 17, 2011
• 年：2011
• 卷：115
• 期：10
• 页码：3942-3948
• 全文大小：922K
• 年卷期：v.115,no.10(March 17, 2011)
• ISSN：1932-7455

文摘

The role of dendrimer structure on the spin density distribution in radical cations was studied for five 1,4-phenylenediamine dendrimers, representing PAMAM-like dendrimer generations ranging from G鈭?.5 to G1.5, in DMSO and MeOH containing TBAPF₆ using in situ ESR UV/vis/NIR spectroelectrochemistry. The radical cations were generated in DMSO by electrochemical oxidation at the first reversible oxidation peak or by AgNO₃ oxidation in DMSO and MeOH. The role of solvation was followed as the dendrimers are in general easier to oxidize in DMSO than in MeOH and the E_1/2 differences were observed to increase with increasing dendrimer generation. In addition, an electrochemically irreversible second oxidation step was observed for the dendrimers in DMSO. Dendrimers terminated by a primary amine tend to block the electrode surface via the follow-up reaction products. The UV/vis/NIR spectra of both the electrochemically and chemically generated radical cations show two intense absorptions in the UV鈭抳is range typical for Wurster鈥檚 type radicals. The radical cations of all PAMAM-like dendrimers give ESR spectra with a g-factor of 2.0031 in DMSO and MeOH solutions. The ESR hyperfine data reflect the localization of the unpaired electron on the redox active PD core of the dendrimers, independent of the type or size of the terminal substituent. The lower resolution of the ESR signals with increasing molecular size points to a strong influence of the core substituents on the molecular-tumbling rate. ENDOR spectroscopy was used for the evaluation of the isotropic hyperfine coupling constants.